© Acta hydrotechnica 24/40 (2006), Ljubljana ISSN 1581-0267 65 UDK/UDC: 519.61/.64:628.35 Prejeto/Received: 3. 4. 2007 Izvirni znanstveni prispevek – Original scientific paper Sprejeto/Accepted: 5. 9. 2008 MERITVE IN MODELIRANJE PROCESNIH VPLIVOV SUBSTRATOV IN FILTER MEDIJEV NA ČISTILNIH NAPRAVAH S PRITRJENO BIOMASO MEASUREMENT AND MODELLING OF PROCESS IMPACTS OF SUBSTRATES AND FILTER MEDIA TO THE OPERATION OF WASTEWATER TREATMENT PLANTS WITH FIXED BIOMASS Darko DREV, Jože PANJAN Substrati in filter mediji se vgrajujejo v čistilne naprave na razli čne na čine, pri čemer imajo lahko bistven vpliv na u činek čiš čenja. Postopke čiš čenja lahko samo intenzivirajo ali pa so glavni nosilci čiš čenja. Do sedaj so se pri projektiranju čistilnih naprav redko izkoriš čali specialni u činki čiš čenja, ki jih lahko dosežemo s substrati in filter mediji. Obi čajno je bil razlog v premajhnem poznavanju teh materialov ter dragi membranski filtraciji. Najbolj zanimive so tehnološke rešitve, pri katerih se izkoristi biološke postopke čiš čenja v kombinaciji z razli čnimi substrati in filter mediji. Na to kažejo tudi izsledki preiskav, ki so podani v tem članku. Pri precejalnikih in rastlinskih čistilnih napravah lahko na primer z ustreznimi substrati odstranimo iz odpadne vode na relativno enostaven na čin fosfor in težke kovine. Ugotovili smo, da dolo čene vrste substratov omogo čajo bistveno ugodnejše pogoje za razvoj bakterijske združbe kot druge. Če se v proces čiš čenja vklju či še membranski filter, se lahko u činkovitost čiš čenja pri enaki velikosti čistilne naprave bistveno izboljša. Na ta na čin lahko iz odpadne vode na relativno enostaven na čin odstranimo tudi viruse, bakterije in težke kovine. Klju čne besede: meritve biomase, modeliranje, čistilne naprave, hranila, CO 2 , pritrjena biomasa, aktivnost mikroorganizmov, rastlinske čistilne naprave Substrates and filter media are built in wastewater treatment plants in various ways, and can have a high impact on their operation effect. As such, they can either only intensify the treatment processes, or they can act as a main treatment carrier. The specific treatment effects, which can be achieved by substrates or filter media application, were until now rarely exploited in the wastewater treatment plants design. The usual reason for this was insufficient knowledge about these materials as well as the high costs of membrane filtration technology. Especially interesting are those technological solutions that use the biological treatment processes in a combination with various substrates and filter media. This can be also seen from the research results provided in this paper. The relatively easy removal of phosphorus and heavy metals from the wastewater, via suitable substrates, can, for example, take place in the percolators and constructed wetlands. It was found that some substrate types provide much more suitable conditions for the development of bacterial communities than others. If the membrane filter is included into the treatment process, then the treatment efficiency of the wastewater treatment plant can be significantly improved, although its size remains the same. Using these techniques, relatively easy removal of viruses, bacteria, and some heavy metals can also be achieved. Key words: measurement of biomass, modelling, wastewater treatment plant, substrate, CO 2 , fixed biomass, microbial mass activity, constructed wetlands 1. UVOD Pri čistilnih napravah sodelujejo razli čni mehanizmi čiš čenja, kot so fizikalni, kemijski in biokemijski procesi čiš čenja (Gray, 1999). 1. INTRODUCTION Wastewater treatment plants include different treatment mechanisms, such as physical, chemical treatment processes and Drev, D., Panjan, J.: Meritve in modeliranje procesnih vplivov substratov in filter medijev na čistilnih napravah s pritrjeno biomaso – Measurement and Modelling of Process Impacts of Substrates and Filter Media to the Operation of Wastewater Treatment Plants with Fixed Biomass © Acta hydrotechnica 24/40 (2006), 65–81, Ljubljana 66 To čno razvrščanje posameznih procesov čiš čenja, še posebej pri komunalnih odpadnih vodah, v eno izmed navedenih skupin je težavno, saj so praviloma pri vsakem procesu prisotni vsi trije mehanizmi. Filtracija vode obsega ve č vrst fizikalnih in kemijskih separacijskih procesov, ki iz vode odstranjujejo ne čisto če (Schweitzer, 1988). Ne čisto če so lahko v obliki delcev ali raztopljenih snovi. Pri fizikalnih procesih filtracije ločimo več vrst mehanizmov zadrževanja delcev. S konvencionalno filtracijo se na filter mediju zadržujejo tisti delci, ki so ve čji od velikosti por. Če gre za zelo fine delce, koloide ali celo raztopljene snovi, govorimo o membranski filtraciji. Pri membranskih filter medijih se v časih u činek filtracije dodatno pove ča z elektri čnim poljem. Takrat govorimo o dializnih membranah. Pri drugi pomembni skupini filter medijev se odstranjujejo ne čisto če na podlagi adsorpcijske sposobnosti filter medijev. Zaradi privla čevanja delcev na površino filter medija zadržuje filter delce, ki so manjši od velikosti por. Pri adsorpciji se vežejo ne čisto če na površino filter medija na podlagi molekularnih privla čnih sil (aktivno oglje, diatomejska zemlja itd.). Tretjo skupino predstavljajo filter mediji, ki kemijsko vežejo ne čisto če iz vode. Najpomembnejši predstavniki tovrstnih filter medijev so ionski izmenjevalci. Membranska filtracija se kot samostojni postopek čiš čenja uporablja v glavnem le za specifi čne tehnološke odpadne vode (oljne emulzije, prisotnost kovin itd.). V kombinaciji z biološkim postopkom čiš čenja pa se lahko uporabljajo membrane za: vpihovanje zraka v aeracijski bazen, zgoščevanje biomase v aeracijskem bazenu, odstranjevanje vode iz blata kot biofilter, za sterilizacijo itd. (Heinrichmeier, 2008). V preteklosti je bila glavna ovira za uporabo membranskih filtrov v kombinaciji z biološkim postopkom čiš čenja hitra zamašitev membran. S sistemom sprotnega odstranjevanja poga če na membranskem filter mediju so ta problem zadovoljivo razrešili (Gründer, 2000). Substrati se lahko v proces biokemijske razgradnje ne čisto č aktivno vklju čijo kot biochemical treatment processes (Gray, 1999). The exact categorisation of treatment processes into only one of the categories given above is difficult, especially in the case of municipal wastewater treatment, since all three mechanisms are regularly present in each process. The water filtration includes several types of physical and chemical separation processes, which remove pollutants from the water (Schweitzer, 1988). The pollutants can be in the form of particles or dissolved matter. The physical filtration processes include several types of particle retention mechanisms. Using the conventional filtration, the particles larger than the size of the pores are retained on the filter media. The membrane filtration is applied in case of very fine particles, colloid particles or in case of dissolved matter. The filtration effect sometimes increases in the membrane filter media due to the electrical field. In such case dialysis membranes are used. Another important category is the filter media that remove the pollutants via their adsorption capability. Since the filter media surface attracts the particles, the filter retains also those particles that are smaller than the size of the pores. During the adsorption process the pollutants bind on the filter media surface through the attractive forces between molecules (activated carbon, diatomaceous earth etc.). The third category is represented by filter media that chemically bind water pollutants. These filter media are best represented by ion exchangers. Membrane filtration is applied as an independent treatment process mainly in specific technological wastewater treatment (oil emulsions, if heavy metals are present etc.). Membranes can be used in a combination with the biological treatment process for: air injection into the aeration tank, sludge thickening in the aeration tank, as a bio-filter, for sterilisation etc. (Heinrichmeier, 2008). The fast clogging of the membranes used to be the main obstacle for the application of membrane filters in the combination with the biological treatment process. This problem, however, has been adequately solved by introducing the simultaneous cake removal (Gründer, 2000). Substrates can be actively involved in the Drev, D., Panjan, J.: Meritve in modeliranje procesnih vplivov substratov in filter medijev na čistilnih napravah s pritrjeno biomaso – Measurement and Modelling of Process Impacts of Substrates and Filter Media to the Operation of Wastewater Treatment Plants with Fixed Biomass © Acta hydrotechnica 24/40 (2006), 65–81, Ljubljana 67 substance, ki kemijsko vežejo dolo čene snovi iz procesa ali ki jih v proces oddajo. Kemijsko aktivne substrate lahko razdelimo v dve glavni skupini: - substrati, ki sodelujejo v procesu čiš čenja z ionsko izmenjavo, - substrati, ki sodelujejo v procesu čiš čenja s kemijskimi reakcijami. Za precejalnike in rastlinske čistilne naprave so primerni predvsem naravni anorganski ionski izmenjevalci, saj so bistveno cenejši od sinteti čnih organskih ionskih izmenjevalcev. Med anorganske ionske izmenjevalce štejemo razli čne naravne glinene materiale, ki imajo sposobnost ionske izmenjeve ter sinteti čne anorganske materiale (Degrémont, 2007). Kot naravna ionska izmenjevalca sta najbolj poznana bentonit in zeolit. Naravni materiali, ki se uporabljajo kot ionski izmenjevalci, imajo običajno amorfno strukturo, medtem ko imajo sinteti čni mikrokristalini čno strukturo. Čiš čenje vode se pri tovrstnih materialih ne vrši zgolj z ionsko izmenjavo, temveč tudi s fizikalnim vezanjem (adsorpcijo). Zeoliti imajo zaradi sposobnosti vezanja ionov in molekul bistveno ve čjo čistilno sposobnost od bentonitov. Tako se na primer vežejo ioni težkih kovin (Pb, Cd, Zn, Cr, Ni, Hg itd.), NH 4 - , H 2 S, Cl 2 itd. Tudi aktivne gline in bentoniti imajo sposobnost vezanja razli čnih ionov, vendar so te lastnosti obi čajno nekoliko slabše izražene kot pri zeolitih. Razne vrste materialov (substratov), na katerih je pritrjena biomasa, lahko reagirajo s posameznimi polutanti v odpadni vodi ali pa tudi ne. Polimerni nosilni materiali v precejalnikih so praviloma kemijsko odporni na vse ne čisto če v odpadnih vodah. Pri re čnem produ, sloju kamnov, žlindri, razli čnih vrstah peskov ter podobnih materialih pa lahko prihaja do kemi čnih reakcij med delci substrata in posameznimi snovmi v odpadni vodi. Reakcije potekajo praviloma med anorganskimi polutanti (fosfati, sulfati, nitrati, nitriti, halogenidi itd.) in ustreznimi anorganskimi snovmi v substratu. Če se kot substrat uporablja nestabilen organski material, kot na primer šota, razne umetne process of biochemical pollutant decomposition as substances that either chemically bind a certain matter from the process, or they emit it into the process. The chemically active substrates can be divided into two main categories: - Substrates used in the treatment process through ion exchange, - Substrates used in the treatment process through chemical reactions. Natural inorganic ion exchangers, which are essentially less expensive than synthetic organic ion exchangers, are especially suitable for percolators and constructed wetlands. Different natural clay materials with ion exchange capability and synthetic inorganic materials belong to the group of inorganic ion exchangers (Degrémont, 2007). Best known natural ion exchangers are bentonite and zeolite. The natural materials, which are used as ion exchangers, usually have amorphous structure, while the synthetic ones have microcrystalline structure. These materials do not clean the water only via ion exchange, but also via physical bonding (adsorption). Zeolites have much higher cleaning capability than bentonites, which is due to their capability of ion and molecule bonding. For example, heavy metal ions are bound in this way: (Pb, Cd, Zn, Cr, Ni, Hg etc.); NH 4 , H 2 S, Cl 2 etc. Active clays and bentonites also have the capability to bind different ions; however, these characteristics are usually less expressed as in the case of zeolites. Various types of materials (substrates), on which the biomass is attached, can either react with certain pollutants in the wastewater, or not. Polymer supporting materials in the percolators are as a rule chemically resistant to all pollutants in wastewaters. However, chemical reactions between substrate particles and particular substances in the wastewater can occur in the case of river gravel, stone layer, scoria, various types of sand and similar materials. Reactions between inorganic pollutants (phosphates, sulphates, nitrates, nitrites, halogenides etc.) and inorganic materials in the substrate regularly take place. If unstable organic material is used as a substrate, such as peat, various artificial soils, or other similar material, then chemical reactions between organic pollutants and Drev, D., Panjan, J.: Meritve in modeliranje procesnih vplivov substratov in filter medijev na čistilnih napravah s pritrjeno biomaso – Measurement and Modelling of Process Impacts of Substrates and Filter Media to the Operation of Wastewater Treatment Plants with Fixed Biomass © Acta hydrotechnica 24/40 (2006), 65–81, Ljubljana 68 zemlje ali kaj podobnega, lahko pride tudi do kemijskih reakcij med organskimi polutanti in substratom (huminske kisline, mle čna kislina, tenzidi, itd.). Možnih reakcij je ve č, odvisno od vrste odpadne vode in vrste substrata. V re čnem produ so lahko na primer sestavine na bazi apnenca. Med apnencem in fosfati lahko poteče reakcija, s katero se fosfor veže iz odpadne vode na substrat. Tako pri precejalnikih in rastlinskih čistilnih napravah, ki imajo substrat na bazi apnenca ali podobnih mineralov, izlo čanje fosforja pogosto ne predstavlja večjih težav. Pri rastlinski čistilni napravi s pritrjenim rastlinjem je pretok odvisen od velikosti in števila vmesnih prostorov med delci substrata, odpadne vode in dolžine poti (Plugge, 2001). Ko se na delcih substrata razvije bakterijska združba, se vmesni prostori med delci substrata še nekoliko zmanjšajo. Plavajo ča bakterijska združba (dispergirana biomasa) lahko prav tako zmanjša hitrost pretoka. Pri rastlinski čistilni napravi je plavajo če bakterijske združbe manj kot 10 %, zato govorimo o čistilni napravi s pritrjeno biomaso. V času rasti imajo velik vpliv na pretok in koncentracije snovi tudi rastline, ki pa jih v tej preiskavi nismo prou čevali. Slika 1 nam shematsko ponazarja tok vode v rastlinski čistilni napravi. substrate can also occur (humic acids, lactic acid, tensides etc.). There are many possible reactions; the type of the reaction depends on the type of wastewater and the substrate. For example, river gravel components can be based on limestone. The reaction, which can take place between the limestone and phosphates, can make the phosphorus from the wastewater to bond on the substrate. Therefore, the phosphorus separation is unproblematic in the percolators and constructed wetlands, where the substrate is based on the limestone or on similar materials. In constructed wetlands with fixed vegetation the flow depends on the size and number of spaces between the substrate particles, on the wastewater, and on the distance (Plugge, 2001). In addition, the spaces between the substrate particles become smaller, after the bacterial community develops on the substrate particles. The floating bacterial community (dispersed biomass) can also reduce the velocity of the flow. Constructed wetlands have less than 10% of bacterial communities; therefore they belong to the wastewater treatment plants with attached biomass. During the growing period the flow is also strongly influenced by plants; these, however, are not included in this investigation. A schematic representation of the flow in a constructed wetland is provided in Figure 1. Slika 1. Shematski prikaz pretoka v rastlinski čistilni napravi v naravi. Figure 1. Schematic representation of flow in a constructed wetland in the nature. Drev, D., Panjan, J.: Meritve in modeliranje procesnih vplivov substratov in filter medijev na čistilnih napravah s pritrjeno biomaso – Measurement and Modelling of Process Impacts of Substrates and Filter Media to the Operation of Wastewater Treatment Plants with Fixed Biomass © Acta hydrotechnica 24/40 (2006), 65–81, Ljubljana 69 Pri rastlinskih čistilnih napravah ima substrat velik vpliv na preto čne koli čine in sposobnost čiš čenje, kar je razvidno iz naslednje Darcyjeve ena čbe (Börner, 1992): In constructed wetlands the substrate has a strong impact on the flow rate and treatment efficiency, which can be seen from the following Darcy equation (Börner, 1992): ds d k F Q v f f Ψ − = = (1) kjer je: v f hitrost filtracije [m/s] Q pretok vode [m 3 /s] k f koeficient pretoka [m/s] dψ/ds potencialni padec [-] F preto čni presek [m 2 ] s pot vode [m] where: v f filtration velocity [m/s] Q flow rate [m 3 /s] k f hydraulic conductivity [m/s] dΨ/ds potential decline [-] F flow section [m 2 ] s flow distance [m] Pri rastlinski čistilni napravi se glavni procesi biokemijske razgradnje vršijo na substratu, na katerem je pritrjena bakterijska združba (EPA, 2000). Ta del je v bistvu polno zapolnjen precejalnik, pri katerem odpadna voda te če, za razliko od ve čine ostalih precejalnikov, v horizontalni smeri. Bakterijska združba bi brez prisotnosti rastlin bistveno slabše razgrajevala ne čisto če, saj rastline vršijo dovajanje kisika in odvajajo nastalo biomaso. Za precejalnike veljajo vsi osnovni mehanizmi biokemijske in kemijske razgradnje ter fizikalni postopki čiš čenja (Panjan, 2006). V odvisnosti od vrste precejalnika so lahko dolo čeni procesi čiš čenja prevladujo či. Če govorimo o čiš čenju (filtraciji), obi čajno mislimo na vse tri procese čiš čenja. Pri naših preiskavah smo pogosto ugotavljali prevladujo če fizikalne in kemijske procese čiš čenja na substratih, saj preiskave niso trajale tako dolgo, da bi se uspeli v zadostni meri razviti vsi mikroorganizmi in s tem povezani procesi biokemijske razgradnje. Precejalniki so lahko polno zapolnjeni z vodo, tako kot je to primer z rastlinsko čistilno napravo s pritrjenim rastlinjem, ali pa se vrši pršenje odpadne vode na vrhu kolone s pritrjeno biomaso. Na sliki 2 je prikazan precejalnik, pri katerem se vrši razprševanje odpadne vode na vrhu kolone. Odpadna voda obliva substrat, na katerem je pritrjena biomasa. The main biochemical decomposition processes, in constructed wetlands, take place on the substrate, which has the bacterial community attached (EPA, 2000). This part actually acts as a completely filled percolator, in which the wastewater flow is horizontal, in contrast to the majority of other percolators. The decomposition of pollutants due to the bacterial community would be much lower without the presence of plants, since the plants bring in the oxygen, and they take away the biomass formed. All basic biochemical and chemical decomposition mechanisms as well as physical treatment mechanisms can take place in the percolators (Panjan, 2006). Depending on the type of the percolator, certain treatment processes may dominate. When the term treatment (filtration) is used, it usually means all three treatment processes. In our research we often investigated the dominating physical and chemical processes of treatment on the substrates, since the duration of the investigations was not long enough for sufficient development of all microorganisms and, in connection with this, not enough for the biochemical decomposition processes. The percolators can be either fully filled with water, such as in constructed wetlands with fixed vegetation, or the sprinkling of the wastewater can take place on the top of the treatment plant. The percolator where the sprinkling of wastewater takes place on the top of the treatment plant is presented in Figure 2. The wastewater passes all over the substrate with the biomass attached. Drev, D., Panjan, J.: Meritve in modeliranje procesnih vplivov substratov in filter medijev na čistilnih napravah s pritrjeno biomaso – Measurement and Modelling of Process Impacts of Substrates and Filter Media to the Operation of Wastewater Treatment Plants with Fixed Biomass © Acta hydrotechnica 24/40 (2006), 65–81, Ljubljana 70 Slika 2. Biokemijski procesi razgradnje pri precejalniku s postopkom razprševanja. Figure 2. Biochemical decomposition processes in the percolator using the sprinkling procedure. Drev, D., Panjan, J.: Meritve in modeliranje procesnih vplivov substratov in filter medijev na čistilnih napravah s pritrjeno biomaso – Measurement and Modelling of Process Impacts of Substrates and Filter Media to the Operation of Wastewater Treatment Plants with Fixed Biomass © Acta hydrotechnica 24/40 (2006), 65–81, Ljubljana 71 V tej shemi je substrat nevtralen, saj služi izklju čno za pritrditev bakterijske združbe. Naše preiskave pa so bile usmerjene v glavnem na specialne substrate, ki se aktivno vklju čujejo v proces čiš čenja. Najve č preiskav smo izvedli pod pogoji, ko je bil substrat potopljen v odpadni vodi. 2. MATEMATI ČNO MODELIRANJE PROCESOV FILTRACIJE IN PRIRASTA BIOMASE Glavni nosilci biokemijskih procesov čiš čenja so bakterije (Gray, 1999). Kemijski procesi čiš čenja pri precejalnikih in rastlinskih čistilnih napravah pa so odvisni tudi od substratov in raznih dodatkov. Kot fizikalne procese pa štejemo: prenos mase, prenos toplote, sedimentacijo, filtracijo itd. Za matemati čno modeliranje procesov smo preskusili ve č ra čunalniških programov, in sicer: MATHCAD, SUPER PRO DESIGNER, GLEAMS – TC, MICROSOFT EXCEL in MATLAB. Po pregledu programov smo se odlo čili za uporabo dveh programov, in sicer: MATLAB za izdelavo zahtevnega modela z možnostjo simulacij in DELPHI 2.0 za program s to čno dolo čenimi zahtevami. Komercialni ra čunalniški SUPER PRO DESIGNER smo prav tako preskusili in ugotovili, da lahko služi le za celovitejšo obravnavo tehnoloških procesov čiš čenja. Pripravljeni meniji v tem programu pa niso dovolj specifi čni za naše potrebe. Osnovne zahteve, ki smo jih upoštevali pri izdelavi lastnih programov: - delo v okolju WINDOWS, - možnost upoštevanja razli čnih vplivov, - možnost vnašanja razli čnih vhodnih parametrov, - možnost prikazovanja razli čnih parametrov, - možnost razli čnih simulacij in - možnost nadgradnje programa. Osnovni mehanizmi delovanja čistilne naprave, ki jih obdelujemo s tem programom, so: 1. Osnovni mehanizem biokemijske razgradnje ne čisto č. Rast mikroorganizmov velja po Monodu (Spitz & Moreno, 1996): The substrate in the figure is neutral and is used only for the fixation of the bacterial community. However, our investigations were oriented towards special substrates, which are actively involved in the treatment process. The majority of studies were done under the conditions, where the substrate was plunged into the wastewater. 2. MATHEMATICAL MODELLING OF FILTRATION PROCESSES AND BIOMASS INCREASE Bacteria are the main carriers of the biochemical treatment processes (Gray, 1999). However, in percolators and constructed wetlands the chemical treatment processes are also dependant on the substrates and various supplements. The following processes are considered as physical processes: mass transfer, heat transfer, sedimentation, filtration etc. Several computer programs were tested for the mathematical modelling of processes: MATHCAD, SUPER PRO DESIGNER, GLEAMS – TC, MICROSOFT EXCEL and MATLAB. After a close review we decided to use two programs: MATLAB for the development of a complex model using simulations, and DELPHI 2.0 as a program covering our exact requirements. We also tested the commercially available SUPER PRO DESIGNER and decided that it could be used only in more comprehensive analyses of technological treatment processes. For our requirements, the program menus are not specific enough. When developing our own programs the main requirements taken into account were: - work in the WINDOWS environment, - consideration of different impacts, - inclusion of different input parameters, - representation of different parameters, - various simulations, and - possibility of program upgrades. The main wastewater treatment plant operating mechanisms to be analysed with this program are: 1. The main mechanism of biochemical pollutant decomposition. According to Monod, the growth of microorganisms is (Spitz & Moreno, 1996): Drev, D., Panjan, J.: Meritve in modeliranje procesnih vplivov substratov in filter medijev na čistilnih napravah s pritrjeno biomaso – Measurement and Modelling of Process Impacts of Substrates and Filter Media to the Operation of Wastewater Treatment Plants with Fixed Biomass © Acta hydrotechnica 24/40 (2006), 65–81, Ljubljana 72 [ ] [ ] dt C d Y dt X d − = (2) (g) matter ble biodegrada used (g) biomass formed (g) snov ljiva biorazgrad porabljena (g) biomasa nastala 0 0 = = − − = C C X X Y (3) 2. Filtracija kot podaljšana longitudinalna disperzija (Panjan, 1998). Za take primere velja naslednja disperzijsko-difuzijska ena čba: 2. Filtration as a prolonged longitudinal dispersion (Panjan, 1998). For such examples the following dispersion-diffusion equation is used: t C x C V x C D ∂ ∂ = ∂ ∂ − ∂ ∂ 2 2 (4) Rešitev te ena čbe se glasi pri začetnih pogojih t = 0, C = C o in robnih pogojih C (0,t) = C 0 . e - γ. t in C ( ∞,t) = 0 takole: The solution to this equation under starting conditions t = 0, C = C 0 and limiting conditions C (0,t) = C 0 . e - γ. t and C ( ∞,t) = 0, is the following: () () ( ) ⎟ ⎟ ⎠ ⎞ ⎜ ⎜ ⎝ ⎛ − + + − − = Dt t x erfc D V x e Dt t x erfc D v x e e C t x C ty 2 2 2 2 2 1 , 0 ξ ξ ξ ξ (5) L t V x + + = ξ (6) kjer je: D longitudinalni (vzdolžni) disperzijski koeficient - v našem primeru konstanten [m 2 /min] C koncentracija raztopine v teko čini [mg/l] V povpre čna hitrost toka [m/min] x koordinata, vzporedna s tokom teko čine [m] t čas [min] γ gostota toka teko čine [m 3 /s] where: D longitudinal dispersion coefficient – in our case it is constant [m 2 /min ] C concentration of the solution in the liquid [mg/l ] V mean flow velocity [m/min ] x co-ordinate parallel to the flow of the liquid [m ] t time [min ] γ liquid flow density [m 3 /s ] Slika 3 prikazuje shemo za matemati čni model, izdelan s programom MATLAB, ki upošteva filtracijo kot podaljšano longitudinalno disperzijo za ena čbo (5). 3. EKSPERIMENTALNI DEL Pri poizkusih smo kot najpomembnejše meritve, poleg klasi čnih parametrov temperature, pH-vrednosti, KPK, BPK5, dušikovih in fosforjevih spojin, merili tudi Figure 3 shows the design of the mathematical model developed using MATLAB, which considers the filtration as prolonged longitudinal dispersion in equation (5). 3. EXPERIMENTAL PART Next to the standard parameters (temperature, pH, COD and nitrogen compounds), measurements of biomass increase, carbon dioxide and biomass activity Drev, D., Panjan, J.: Meritve in modeliranje procesnih vplivov substratov in filter medijev na čistilnih napravah s pritrjeno biomaso – Measurement and Modelling of Process Impacts of Substrates and Filter Media to the Operation of Wastewater Treatment Plants with Fixed Biomass © Acta hydrotechnica 24/40 (2006), 65–81, Ljubljana 73 prirast biomase, nastanek ogljikovega dioksida in aktivnosti biomase. Na sliki 5 je prikazana pilotna naprava, na kateri smo meritve opravili. V prekate smo dajali substrate (re čni prod, zeolit, keramiko, steklo, šoto, vermikulit itd.) in odpadno vodo spuš čali preko naprave na razli čne na čine. V velikih komorah P1, P2 in P3 smo imeli re čni prod, v komore 1, 2, 3 in 4 pa smo dodajali specialne substrate. Pred dodajanjem specialnih substratov smo spuš čali prek čistilne naprave samo grezni čno odpadno vodo, da se je na pesku kot substratu formirala ustrezna bakterijska združba. Nato smo dodajali specialne substrate. Aktivnost mikrobne biomase smo merili z metodo pretvorbe INT (jodo-nitro-tetrazolijevega klorida) v formazan. were performed in the experiments. The pilot plant, on which the measurements were done, is presented in Figure 5. The substrates were introduced into the chambers (river gravel, zeolite, ceramics, glass, peat, vermiculite etc.), while the sewage was passed through the device in different ways. Large chambers P1, P2 and P3 were introduced with river gravel, and chambers 1, 2, 3 and 4 were introduced with special substrates. Before the addition of special substrates, drain sewage was passed through the water treatment plant so that the bacterial community formed on the sand (as substrate). Then we added special substrates. The activity of the microbe biomass was measured using the conversion of INT (iodo-nitro-tetrazolium chloride) in the formazan. Slika 3. Matemati čni model, izdelan s programom MATLAB, ki upošteva filtracijo kot podaljšano longitudinalno disperzijo za ena čbo (5). Figure 3. Mathematical model developed using the MATLAB program, which considers filtration as prolonged longitudinal dispersion for equation (5). Drev, D., Panjan, J.: Meritve in modeliranje procesnih vplivov substratov in filter medijev na čistilnih napravah s pritrjeno biomaso – Measurement and Modelling of Process Impacts of Substrates and Filter Media to the Operation of Wastewater Treatment Plants with Fixed Biomass © Acta hydrotechnica 24/40 (2006), 65–81, Ljubljana 74 Slika 4. Prikaz uporabe lastnega programa za izra čune in izris krivulj razgradnje ne čistoč z upoštevanjem enačb (2) in (3). Figure 4. Application of our own program for computing and curve drawing , following equations (2) and (3). Slika 5. Shema pilotne naprave. Figure 5. Pilot plant scheme. 3.1 MERJENJE BIOMASE V PREKATIH ČISTILNE GREDE, NAPOLNJENE Z RE ČNIM PRODOM IN ZEOLITOM Prekati P1, P2, P3 in P4 so bili napolnjeni z re čnim prodom. Prekati V2, V3 in V4 so bili napolnjeni z zeolitom. Zeolit smo v te prekate spustili v vre čah iz plasti čne mreže. Postopek merjenja biomase je potekal tako, da smo po dolo čenih časovnih terminih odvzeli vzorce s substratom in jih žarili. 3.1 BIOMASS MEASUREMENT IN THE TREATMENT POND CHAMBERS FILLED WITH RIVER GRAVEL AND ZEOLITE The chambers P1, P2, P3 and P4 were filled with river gravel. The chambers V2, V3 and V4 were filled with zeolite. Bags made of plastic net and filled with the zeolite were put into these treatment pond chambers. In the biomass measurement process the samples containing the substrate were first sampled in certain time intervals, and ashed afterwards. Drev, D., Panjan, J.: Meritve in modeliranje procesnih vplivov substratov in filter medijev na čistilnih napravah s pritrjeno biomaso – Measurement and Modelling of Process Impacts of Substrates and Filter Media to the Operation of Wastewater Treatment Plants with Fixed Biomass © Acta hydrotechnica 24/40 (2006), 65–81, Ljubljana 75 [ mg/g substrate biomass substrat biomasa S C B A − ] − = = (7) kjer je: A teža biomase pri 110 0 C [mg] B teža biomase pri 550 0 C [mg] C teža substrata [g] S substrat kot slepi preskus [g] where: A biomass weight at 110 o C [mg] B biomass weight at 550 o C [mg] C substrate weight [g] S reference substrate [g] Iz grafikona na sliki 6 je razvidno, da se je na razli čnih substratih, pod razli čnimi pogoji, razvila razli čna koli čina biomase. Odve čna biomasa odpada iz substrata, zato se v dolo čenih časovnih intervalih pojavljajo tudi negativni prirastki biomase. The graph on Figure 6 shows how different biomass amounts developed on different substrates and under different conditions. Since the surplus biomass falls off from the substrate, the negative increase of biomass also occurs in certain time intervals. Slika 6. Prikaz vsebnosti biomase na substratu v [mg/g]. Figure 6. Amount of biomass on the substrate [mg/g ]. 3.2 MERJENJE KOLI ČINE OGLJIKOVEGA DIOKSIDA V POSAMEZNIH PREKATIH MODELA ČISTILNE GREDE, NAPOLNJENE S SUBSTRATOMA RE ČNI PROD IN ZEOLIT Količino ogljikovega dioksida smo merili z dvema metodama (Cooper, 2004): z metodo neposrednega merjenja smo dolo čili raztopljeni kisik v 100 ml vode iz posameznega prekata modela. Dodali smo 1 do 3 kaplje fenolftaleinskega indikatorja in titrirali z 0,1 N NaOH do pojava rde čkaste barve. Vsebnost CO 2 v odpadni vodi smo 3.2 MEASUREMENTS OF CARBON DIOXIDE AMOUNT IN CERTAIN AREAS OF THE TREATMENT POND MODEL FILLED WITH RIVER GRAVEL AND ZEOLITE SUBSTRATES The amount of carbon dioxide was measured using two methods (Cooper, 2004): using the method of direct measurement we determined the amount of dissolved oxygen in 100 ml of water from the particular chamber of the model. We added 1 to 3 drops of phenolphthalein indicator, and titration with 0.1 N NaOH was performed until the appearance of red colour. The content of CO 2 Drev, D., Panjan, J.: Meritve in modeliranje procesnih vplivov substratov in filter medijev na čistilnih napravah s pritrjeno biomaso – Measurement and Modelling of Process Impacts of Substrates and Filter Media to the Operation of Wastewater Treatment Plants with Fixed Biomass © Acta hydrotechnica 24/40 (2006), 65–81, Ljubljana 76 dolo čili po naslednji formuli: ml pri titraciji x 44 = mg / l ogljikovega dioksida. Pri metodi z barijevim hidroksidom smo dolo čali koli čino ujetega CO 2 , ki se ujame v plastenko nad sedimentom v 24 urah. Plastenko s približno 1,5 l smo odrezali v spodnjem delu in jo pogreznili v sediment, tako da je bil rob pod vodno gladino. Skozi zamašek smo namestili cev, skozi katero smo po 24 urah z akvarijsko črpalko iz črpali nabrane pline skozi posodo z raztopino Ba Cl 2 . Posamezne posode smo nato prepihali z dušikom in titrirali z 0,05 N HCl, tako da smo najprej dolo čili fenolftaleinski preskok od rdeče v brezbarvno, nato pa preskok metil oranžnega indikatorja (MO) od zelenkaste barve v čebulno barvo. Koli čino sproš čenega oziroma v plastenko ujetega CO 2 v 24 urah smo izra čunali po naslednji formuli: titracija (MO) v ml x 0,05 x 44 = mg CO 2 . Iz grafikona slike 7 je razvidno, da so bili procesi biokemijske razgradnje odpadne vode razli čni pri razli čnih substratih. Pri tem so imeli velik vpliv na te procese tudi drugi pogoji (razli čni prekati). in the wastewater was determined according to the equation: ml used in titration x 44 = mg/l of carbon dioxide. Secondly, using the barium hydroxide method we determined the amount of CO 2 captured in the plastic bottle under the sediment, during the period of 24 hours. The bottom part of the approximately 1.5 l plastic bottle was cut and pushed into the sediment, in a way that the brim was under the water surface. A pipe was fixed through the plug, through which we pumped out the accumulated gasses during the period of 24 hours, using an aquarium pump. The gasses were pumped through the vessel containing BaCl 2 solution. The separate vessels were then flushed out with nitrogen and titrated with 0.05 N HCl. The titration was done in a way that we first determined the phenolphthalein change of colour from red to colourlessness, and then the methyl orange (MO) indicator colour change from green to onion colour. The amount of the evolved CO 2 , or better the amount of CO 2 caught during the period of 24 hours, was calculated using the equation: titration (MO) in ml x 0.05 x 44 = mg CO 2 . The graph on Figure 7 shows that the biochemical wastewater decomposition processes were different in the case of different substrates. In addition, other conditions (different chambers) also had a strong impact on these processes. Slika 7. Koli čina sproš čenega CO 2 v modelu z BaCl 2 . Figure 7. Amount of evolved CO 2 in certain areas of the treatment pond model using BaCl 2 . Drev, D., Panjan, J.: Meritve in modeliranje procesnih vplivov substratov in filter medijev na čistilnih napravah s pritrjeno biomaso – Measurement and Modelling of Process Impacts of Substrates and Filter Media to the Operation of Wastewater Treatment Plants with Fixed Biomass © Acta hydrotechnica 24/40 (2006), 65–81, Ljubljana 77 3.3 MERJENJE AKTIVNOSTI MIKROBNE MASE PRI RAZLI ČNIH SUBSTRATIH IN RAZLI ČNIH OBREMENITVAH V POSAMEZNIH PREKATIH MODELA ČISTILNE GREDE V prekate, v katerih se je nahajal pesek, smo namestili plastično cev s premerom 10 cm, ki je bila v predelu, ki je bil zakopan v pesek, perforirana. Na cev smo namestili plastenko s preluknjanim zamaškom, v katerega smo vstavili cevko, ki je vodila do stekleni čke z barijevim hidroksidom (Ba(OH) 2 ). Ves sistem je bil zatesnjen z lepilom. V prekate, ki so se nahajali za prekati, napolnjenimi s peskom, v katerih je bila le teko čina, smo potopili plasti čne vre čke, napolnjene s peskom in ostalimi substrati: steklene kroglice; drobljena keramika; šota; tufko, zmešan s peskom v razmerju 1 : 1; aktivno oglje, zmešano s peskom v razmerju 1 : 1, in agrogel, zmešan s peskom v razmerju 1 : 100. Vsak preskus z dolo čeno odpadno vodo je trajal en teden. Na koncu dovajanja grezni čne vode smo odvzeli prvi vzorec, na koncu dodajanja hranilne juhe pa drugi vzorec. V naslednjem poskusu smo kot glavno hranilno snov uporabili 1 % sladkorno raztopino, vzor čenje pa je bilo izvedeno tako v začetku (grezni čna voda) kot po koncu dodajanja sladkorja. Produkcijo ogljikovega dioksida smo merili v 24-urnih intervalih v treh prekatih, napolnjenih s peskom, z metodo z barijevim hidroksidom. Koli čino sproščenega oziroma v plastenko ujetega CO 2 in oborjenega z barijevim hidroksidom smo dolo čili tako, da smo vzorce titrirali z 0,05 M HCl. Slika 8 prikazuje aktivnost mikrobne biomase, ki uporablja acetat kot vir energije za razli čne substrate, ki so bili obešeni v vre čkah za vsakim prekatom s peskom, slika 9 pa prikazuje aktivnost mikrobne biomase v 1.10-9 O 2 ml/(g.h) v treh prekatih, v katerih je hranivo sladkor. 3.3 MEASUREMENTS OF MICROBIAL MASS ACTIVITY AT DIFFERENT SUBSTRATES AND DIFFERENT LOADINGS OF INDIVIDUAL AREAS OF THE TREATMENT POND MODEL The chambers introduced with sand were fitted with a plastic pipe with a diameter of 10 cm. The part of the pipe buried into the sand was perforated. A plastic bottle with a drilled plug was fixed on the pipe. We fixed a smaller pipe into the plug, which was connected with the vessel containing barium hydroxide (Ba(OH) 2 ). The system was tightened with glue. Into the other areas containing only water, which were located behind the areas containing sand, the plastic bags filled with sand and other substrates were dipped: small glass balls; crushed ceramics; peat; tufko (material based on zeolite) mixed with sand in the ratio 1 : 1; active carbon mixed with sand in the ratio 1 : 1; and agrogel (material based on synthetic polymers) mixed with sand in the ratio 1 : 100. The duration of each experiment with particular wastewater was one week. At the end of the application of the municipal wastewater the first sample was taken, and at the end of adding nutrient broth the second one was taken. The main nutritive substance used in the next experiment was 1% sugar solution. The sampling was done in the beginning (municipal wastewater) as well as after the addition of sugar. In three areas filled with sand the carbon dioxide production was measured after 24-hour intervals, using the barium hydroxide method. The amount of evolved CO 2 , or actually, the amount of CO 2 caught in the plastic bottle, and precipitated using barium hydroxide, was determined with titration of the samples using 0.05 M HCl. Figure 8 shows the activity of microbial biomass, which uses acetate as energy source, in 1.10-9 O2 ml/(g.h), for different substrates that were hung in the bags behind each area containing sand, while Figure 9 shows the activity of microbial biomass in 1.10-9 O 2 ml/(g.h) in areas where sugar was used as nutrient. Drev, D., Panjan, J.: Meritve in modeliranje procesnih vplivov substratov in filter medijev na čistilnih napravah s pritrjeno biomaso – Measurement and Modelling of Process Impacts of Substrates and Filter Media to the Operation of Wastewater Treatment Plants with Fixed Biomass © Acta hydrotechnica 24/40 (2006), 65–81, Ljubljana 78 Slika 8. Aktivnost mikrobne biomase, ki uporablja acetat kot vir energije v 1.10 -9 O 2 ml/(g .h), za različne substrate. Figure 8. Activity of microbial biomass, using acetate as energy source, in 1.10 -9 O 2 ml/(g.h), on different substrates. Slika 9. Aktivnost mikrobne biomase v 1.10 -9 O 2 ml/(g .h) v treh prekatih, v katerih je hranivo sladkor. Figure 9. Activity of microbial biomass in 1.10 -9 O 2 ml/(g.h) in three areas, where sugar is used as nutrient. Raziskave so pokazale, da se na posameznih substratih razvije bistveno ve č bakterijske združbe kot na drugih (preglednica 1). Ekspandirano steklo se je pokazalo kot najbolj ugodna podlaga za razvoj mikroorganizmov. Tudi re čni prod in porozna keramika sta dala dobre rezultate. The studies have shown that the bacterial community developed considerably more on certain substrates than on others (Table 1). Expanded glass proved to be the most suitable substrate for microorganism development. River gravel and porous ceramics also yielded good results. Drev, D., Panjan, J.: Meritve in modeliranje procesnih vplivov substratov in filter medijev na čistilnih napravah s pritrjeno biomaso – Measurement and Modelling of Process Impacts of Substrates and Filter Media to the Operation of Wastewater Treatment Plants with Fixed Biomass © Acta hydrotechnica 24/40 (2006), 65–81, Ljubljana 79 Preglednica 1. Razvrstitve najve čje do najmanjše aktivnosti biomase na posameznem substratu glede na aktivnost v vseh prekatih. Table 1. The categorisation, from highest to lowest, of biomass activity on individual substrates, according to the activities in all areas. substrat – Substrate 1. mesto 1 st place 2. mesto 2 nd place 3. mesto 3 rd place 4. mesto 4 th place 5. mesto 5 th place 6. mesto 6 th place 7. mesto 7 th place steklo – Glass 3 x 2 x 1 x pesek – Sand 1 x 3 x 2 x tufko – Tufko 2 x 3 x 1 x agrogel – Agrogel 1 x 1 x 2 x 2 x keramika – Ceramics 2 x 1 x 2 x 1 x šota – Peat 1 x 1 x 1 x 3 x oglje – Active carbon 6 x 4. RAZPRAVA Izbira substrata ima lahko velik vpliv na učinek čiš čenja na čistilnih napravah s pritrjeno biomaso in v rastlinskih čistilnih napravah. Aktivnost mikrobne biomase je namreč pogojena z izbiro substrata. Vseh vplivov substratov za sedaj še ni možno to čno kvantificirati, saj ne poznamo vseh mehanizmov delovanja posameznega materiala na procese biokemijske razgradnje na substratu zgrajene biomase. Danes se že raziskujejo tudi nekatere lastnosti t. i. “informiranih” substratov s spominom (iz keramičnih in steklenih materialov), ki dodatno pospešujejo procese biokemijske razgradnje (Panjan, 2006). Poleg eksperimentalnih meritev smo razvili še osnovne matemati čne modele, ki jih lahko po potrebi nadgrajujemo. Za opis procesa filtracije, kot procesa čiš čenja na biofiltru, smo uporabili model s podaljšano longitudinalno disperzijo s programom Matlab. Ta že v osnovi zajema procese biokemijske razgradnje in fizikalnega čiš čenja. Pri takšnem modelu je pomembno samo to, kaj v čistilno napravo priteče in kaj odte če. Z drugimi besedami, ni pomembno kateri procesi sodelujejo pri čiš čenju. Če postopku čiš čenja naknadno dodamo še membranski filter, lahko iz vode na enostaven in direkten način odstranimo še ve čje količine organskih ne čisto č. Na ta na čin lahko še 4. DISCUSSION In the wastewater treatment plants with biomass attached to the substrate, the choice of the substrate has a strong impact on the effectiveness of the treatment plant. The microbial biomass activity depends on the substrate type. It is currently not possible to quantify all substrate impacts, since all of the operating mechanisms on the biochemical decomposition processes of the particular material are not known. The so-called “informed” substrates with memory, which additionally speed up the biochemical decomposition processes, are a separate topic (Panjan, 2006). It is possible to build such “information” into ceramic and glass mater- ials. We have developed main mathematical models, which can be upgraded if necessary. The analysis of the biofilter treatment processes as a prolonged longitudinal dispersion using Matlab program. This in its basis includes all processes of biochemical decomposition and physical treatment. In such model the only thing important is what flows in and out from the treatment plant. Or, in other words, it is not important which mechanism is responsible for the treatment. If a membrane filter is additionally included in the treatment process, the large amount of suspended organic pollutants can be easily and directly separated from the treatment process. This can increase the further treatment Drev, D., Panjan, J.: Meritve in modeliranje procesnih vplivov substratov in filter medijev na čistilnih napravah s pritrjeno biomaso – Measurement and Modelling of Process Impacts of Substrates and Filter Media to the Operation of Wastewater Treatment Plants with Fixed Biomass © Acta hydrotechnica 24/40 (2006), 65–81, Ljubljana 80 dodatno izboljšamo u činkovitost čiš čenja ob nespremenjeni velikosti čistilne naprave. 5. ZAKLJU ČKI S poizkusi smo dokazali, da nam dolo čene vrste substratov omogo čajo bistveno ugodnejše pogoje za razvoj bakterijske združbe kot druge, kar je lahko prav tako pomemben parameter pri projektiranju čistilne naprave. Ugotovili smo, da sta se najintenzivneje razvijala mikrobna biomasa na ekspandiranem steklu in na kerami čnem substratu. Tudi re čni prod je dal ugodne rezultate. Steklo in keramika se po kemi čni sestavi bistveno ne razlikujeta, zato ju lahko uvrstimo v širšo skupino anorganskih substratov. Mnenja smo, da je možno razviti takšen stekleni ali kerami čni material, ki bo zagotavljal še ugodnejše pogoje za razvoj mikrobne biomase. V praksi se kot nosilci mikrobne biomase največ uporabljajo polimerni materiali (PE, PP, itd.). To so kemijsko in fizikalno inertni materiali do mikrobne biomase in nečisto č v vodi, zato ne pospešujejo biokemijskih procesov razgradnje. Obi čajno imajo tudi bistveno manjšo površino, kot jo lahko dobimo s poroznimi kerami čni materiali ali z ekspandiranim steklom. Z izdelanimi matemati čnimi modeli smo simulirali osnovne procese filtracije in prirasta biomase. effectiveness, although the size of treatment plant remains the same. 5. CONCLUSIONS The experiments have shown that certain substrate types can provide much more suitable conditions for the development of bacterial community than others. This can be an important parameter in wastewater treatment plant design. It was established that the microbial biomass development was most intensive on expanded glass, followed by ceramic substrate. The river gravel also gave good results. According to their chemical composition, glass and ceramics do not differ considerably. Therefore, they can be categorised into the broader category of inorganic substrates. Our opinion is that it is possible to develop such glass or ceramic material that would guarantee even more suitable conditions for the microbial biomass development. In practice, mainly polymer materials (PE, PP etc.) are used as a support for the microbial biomass. These materials are chemically and physically inert to the microbial biomass and to pollutants in the water. Therefore, they do not speed up the biochemical decomposition processes. Usually they have much smaller surfaces than porous ceramics or expanded glass. With the mathematical models developed, we simulated the basic processes of filtration and biomass increase. 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Wechselwirkungen industrieller organischer Schadestoffe mit Rhizosphärenkomponenten und Bilanzierung von Stoffströmen in Pflanzenkläranlagen – Laborversuche, Dissertation, Universität Leipzig, 165 p. (http://www.ufz.de/data/ufzbericht15-01524.pdf) Schweitzer, P.A. (Ed.) (1997). Handbook of Separation Techniques for Chemical Engineers, McGraw Hill, New York, 1356 p. Naslova avtorjev – Authors' Addresses dr. Darko Drev Inštitut za vode Republike Slovenije – Institute for Waters of the Republic of Slovenia Hajdrihova 28, SI-1000 Ljubljana, Slovenia E-mail: darko.drev@izvrs.si & Univerza v Ljubljani – University of Ljubljana Fakulteta za gradbeništvo in geodezijo – Faculty of Civil and Geodetic Engineering Inštitut za zdravstveno hidrotehniko – Institute of Sanitary Engineering Jamova c. 2, SI-1000, Ljubljana, Slovenia izr. prof. dr. Jože Panjan Univerza v Ljubljani – University of Ljubljana Fakulteta za gradbeništvo in geodezijo – Faculty of Civil and Geodetic Engineering Inštitut za zdravstveno hidrotehniko – Institute of Sanitary Engineering Jamova c. 2, SI-1000, Ljubljana, Slovenia E-mail: joze.panjan@fgg.uni-lj.si